Influenza causative agent

The causative agent of influenza is a microorganism that, when it enters a living organism, can cause the reproduction of its own cells in the tissues of the epithelial lining of the upper respiratory tract, causing a violation of the integrity of the cells and their death. Through damaged epithelial barriers, the virus enters the bloodstream and spreads throughout the body. Influenza is a particularly dangerous infectious disease that causes epidemics among the population almost every year. ^[1]. Almost every flu epidemic takes on the character of a real natural disaster, causing great damage to public health. All populations are affected, but pregnant women, children aged 6-9 months, the elderly, and people with chronic diseases are most at risk of developing complications.

The causative agent of influenza is a virus that can very often change its antigenic structure, which leads to the fact that a person’s immunity formed after one illness does not protect against re-infection with influenza of another antigenic structure (another strain). Bacteria are not the causative agents of influenza infection, they can accumulate on a weakened body, causing numerous and severe bacterial complications.

Types of infection

Influenza virus belongs to the genus Influenzavirus, belongs to the family of RNA-containing orthomyxoviruses Orthomyxoviridae. According to the difference in their own antigens, influenza viruses are divided into types A, B and C. ^[2].

The most dangerous in this type of virus is its tendency to antigenic variability, which leads to the failure of the developed immunity in the first case of infection. In other words, if a person has been ill with the flu, he has developed immunity to this type (strain) of the virus, but in a short period of time the virus has changed somewhat and for the body it is already becoming a new disease that will be as difficult to tolerate as the previous one.

Among people, viruses spread by airborne droplets – the fastest and most contact way, leading to epidemic situations. ^[3]. Excretion occurs with saliva and sputum when coughing, sneezing, talking, which in the form of a fine aerosol spread in the air and are inhaled by other people. In some cases, it is possible to implement a contact-household transmission route, namely through dishes and toys. The ability to mutate and the high contagiousness of influenza forces scientists to constantly work on new, more effective vaccines against the disease in order to prevent the outbreak of new epidemics.

Type A influenza viruses are considered the most dangerous. ^[4]. They are able to hit not only people, but also birds and animals. A-viruses have high pandemic properties due to the fact that 2 antigens in their composition can constantly mutate. The formula of the influenza virus consists of two subtypes of surface antigens – hemagglutinin, which ensures that the infection enters and fixes in the cells of the human body, and neuraminidase, which ensures the processes of virus reproduction in the cell and its subsequent migration to other human cells. So, in the H1N1 swine flu formula, the letter H stands for the hemagglutinin antigen, and the letter N stands for neuraminidase.

These antigens are easily and quickly modified, leading to the constant emergence of new strains of influenza. In the modern world, there are about 2 thousand strains of this virus. This explains the annual outbreaks of epidemics of this infection in all parts of the world. Scientists have not yet figured out the reasons for this ability to modify the virus, so it is currently impossible to stop this process. At the same time, A-type viruses provoke an epidemic situation every 2-3 years, B-type viruses do it less often – 1 time in 4-6 years, and C-type viruses are not epidemiologically dangerous.

Thus, type A influenza is considered the most dangerous and capable of variability. It is influenza A viruses that are responsible for the emergence of pandemics and severe epidemics. It is very stable, it can be stored at 40 degrees for 2-3 weeks, which makes it hazardous to human health. For comparison, the rest of the influenza serotypes cannot withstand the temperature already at 37-37,5 degrees and die.

The variability of the A-virus occurs when the parameters of hemagglutinin and neuraminidase change. So, the variability of hemagglutinin by point mutations in a gene is called antigenic drift. ^[5]. If a complete replacement of the gene occurs, then an antigenic shift occurs. This causes not just a high incidence, but real pandemics, like the one that happened in the world at the beginning of the 20th century and is known as the “Spanish Flu”.

Less dangerous to humans, but no less significant in nature, are influenza viruses of types B and C. Only the B-type virus can change in the drift type, the C-type virus remains unchanged. This indicates that only A and B-type viruses can participate in epidemic situations.

Any influenza virus must have its own territory in order to survive. For all of them it is living organisms. Type A influenza can survive in humans and animals, while influenza types B and C can only survive in humans. At the same time, many of these viruses can exist in the external environment for up to 4 hours. Influenza A-type is the most resistant to survival, sometimes it can survive in a dried drop on bedding for 10-11 days. Room dust can keep influenza A-type as long as 5 weeks at certain temperatures. Influenza viruses die during wet cleaning with the use of any antiseptic agents. In order to kill all the remnants of the virus in the room where the flu patient was, it is enough just to ventilate it.

New viruses

Among the newest flu strains in 2017-2018, the most prominent is the Michigan influenza virus, which is a subtype of the swine flu virus (A/Michigan/45/2015 (N1H1)) ^[6]. Such a name code helps scientists to easily understand in what year a given strain was first discovered, and what antigenic structure they have to deal with. All this facilitates diagnostic measures in patients and the appointment of effective therapy.

It is already known that the Michigan virus has a high probability of various complications. Also, this strain is very contagious, which can lead to numerous epidemics. Mutations of this strain are explained by the fact that it is able to extract new genes from animal organisms into which it enters, surviving in them, but not causing infection.

The Michigan virus, penetrating into a human cell, will rearrange the code of its DNA, using life-supporting properties for its own replication. At the same time, the virus genes amplify human proteins, which as a result increase the aggressiveness of the impact of influenza on the human body and prevent its decay.

The most important factor in the recovery of a patient with Michigan flu is how quickly he went to the doctor at the initial stage of the disease.

The main manifestations of this strain of the disease include:

• the incubation period is from 2 hours to a week, most often it lasts up to 72 hours;
• a sharp onset of the disease, which will be the more intense, the higher the concentration of the virus that simultaneously enters the human body;
• extremely high body temperature from the very beginning of the disease, reaching 39-41 degrees;
• pronounced signs of intoxication – weakness, drowsiness, weakness, aches, headaches;
• in severe cases, signs of encephalopathy with convulsive seizures, hallucinations, vomiting, as well as vascular disorders, manifested by nosebleeds, pinpoint hemorrhages in the soft palate.
• the presence of hyperemia of the mucous membranes of the eyes and puffiness of the face;
• the presence of burning pain in the sternum;
• the occurrence of nasality, nasal congestion without typical manifestations of the common cold.

The symptoms of the Michigan flu will be expressed as much as the immune system of the sick person feels at the time of the encounter with the infection. If a person has chronic diseases, he will most likely endure the Michigan flu quite hard.

To protect against this strain of influenza, a new super-effective vaccine has already been developed, the vaccination of which will help not to get sick with the infection and protect yourself from many of the most serious complications that it leads to.

Ways of infection

Influenza is an easily transmitted disease that spreads in the air masses from person to person. ^[7]. The most dangerous for others are those who are already infected with the virus, even if the incubation period has not yet expired and the person himself does not yet feel sick. After the onset of symptoms of the disease, the infectiousness remains at a high level for up to 7 days, and then decreases several times, however, the patient becomes completely epidemiologically safe only after 10-14 days from the onset of symptoms.

The airborne way of spreading influenza leads to the fact that the disease forms epidemics, to which small children, pregnant women, the elderly, and people suffering from chronic diseases are especially sensitive. These categories of people can become infected even when in contact with a small amount of the virus.

Influenza is also transmitted from person to person and by household contact, through household items, dishes, hygiene products. In order to ensure that when one sick person is identified, those who live and are constantly close to him do not suffer, doctors advise isolating the patient, providing him with separate household items, dishes and towels.

In the air, influenza can survive without a human body from 2 to 9 hours, on paper – from 8 to 12, and on metal – 24-28 hours. After entering the human body on the respiratory mucosa, viruses attach to the cell with the help of hemagglutinin. The enzyme neuraminidase destroys the mucosal cell membrane, and the virus enters the cell, destroying it. Viral RNA replication and assembly of viral particles take place. New viruses are released and infect other cells. Some of the virus that has entered the body remains in place, coming out when talking, coughing, sneezing, and infect others in this way.

Seasonality of influenza virus

Influenza infection has a seasonal distribution among people, since the survival of its particles directly depends on air temperature and humidity. The risk of epidemics is highest at temperatures from +5 to -5, when a decrease in air humidity creates favorable conditions for the penetration of viruses into the human body, due to cooling and dryness of the respiratory tract ^[7][9].

Also contributes to the “prosperity” of the infection low solar activity and lack of vitamin D in the surrounding space.

In the period from autumn to spring, the virus spreads easily in the environment, gradually affecting entire groups of people. High-risk groups also include schoolchildren and students in secondary specialized educational institutions, medical personnel of medical institutions, transport and service workers. This should also include military units, barracks, where optimal conditions are created for the transmission of the pathogen. Influenza spreads when sneezing or coughing at a distance of about 3,5 meters.

Already infected people (virus carriers) act as a source of infection. If a new or mutated strain of influenza arrives in a region in a particular period of time, then its accelerated spread with the formation of epidemics is possible.

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